crop cultivation Grower 101: RootingRooting hormones are essential forHormones some crops; find out which ones, which hormones to use and how to use them. By Christopher Cerveny and James Gibson The quick dip is a popular technique used to apply rooting hormones. (Photo courtesy of Christopher Cerveny) egetatively propa- Perhaps the situation in which available containing one or both of tip. Fully developed flowers on cut- gated floriculture rooting hormones are best utilized them (see Figure 2, page 38). tings are sometimes another sign crops continue to is in propagation of the “new and that tissue may be too old to root± increase in popu- unusual.” In today’s marketplace CULTURAL PRACTICES optimally. Mist and light levels larity because of customers are oftentimes demand- Plant response to rooting hor- tremendous production, marketing ing new products faster than they mones varies with each species, but and garden success. Growers are can be developed; the green before rooting hormones are intro- able to propagate a wide variety of industry is no stranger to this phe- duced, growers should implement herbaceous plants on-site through nomenon. Rooting hormones can a few simple cultural practices to theV help of improved stock plant improve the visibility of temperate reduce the number of propagation management techniques and prop- and tropical annual and perennial challenges. Cuttings, whether they agation protocols set by industry species by increasing propagation are grown from on-site or off-shore standards and university research success. Common or prized stock plants, should be thoroughly programs. However, moderate and woody ornamental groups such as inspected before planting. difficult-to-root plant species can vines, groundcovers and flower- Softwood cuttings that have an prevent producers from realizing ing shrubs add a multitude of new actively growing shoot tip should their full potential as propagators. possibilities to a grower’s plant be selected. Tissues that are too Application of auxin-based, com- inventory. young or too old will root more mercially available rooting hor- slowly than cuttings that are at the mones may be the key to overcom- AUXIN proper stage of maturity. Cuttings ing this challenge, which Auxin is a plant hormone that that are too old also tend not to ultimately leads to an increase in aids in the initiation of adventitious branch as well as younger, softer product diversity. See Figure 1, roots. Indole acetic acid (IAA) is the tissue. Therefore, it is important to right, for a list of species that may naturally occurring auxin found in visually inspect the lower portion benefit from a rooting hormone plants. IAA is involved in nearly of the cutting to check for woody Top: Crops such as argyranthemum may application. every aspect of plant growth and tissue that is brown or grayish- benefit from an application of rooting In general, the application of development. Some of the process- brown in color. Cuttings that exhib- hormone. Bottom: Rooting hormones may improve uniformity of cuttings in rooting hormones is not required es regulated by IAA include forma- it this hardwood tissue may need propagation trays. (Photos courtesy of for most herbaceous species. The tion of embryo in development, to be trimmed closer to the shoot James Gibson) added labor cost of application is induction of cell division, stem and not necessary with easy-to-root cleoptile elongation, apical domi- Figure 1. Requirement levels of rooting hormones for a select group of floriculture crops. cuttings; however, propagation of nance, induction of rooting, vascu- None Optional Essential moderate and difficult-to-root lar tissue differentiation, fruit Angelonia Argyranthemum Bougainvillea species with rooting hormones development, and tropic move- Bacopa/sutera Calibrachoa Brachyscome may enhance rooting percentages. ments such as bending toward Coleus Diascia Dahlia Exogenously applied hormones light. Synthetic forms of auxin are Cuphea Nemesia Heliotrope also facilitate rooting where cul- available commercially in the form Impatiens Salvia (certain species) Hibiscus, tropical tural practices or environmental of Indolebutyric acid (IBA) and New Guinea impatiens Scaevola Lobelia conditions are not ideal. Examples napthaleneacetic acid (NAA). Petunia Snapdragon Mandevilla include uneven misting, subopti- Commercial preference given to Perilla Fuschia Mimulus mal propagation temperatures these synthetic compounds and Plectranthus Strobilanthes Osteospermum and, in some cases, reduced light less to IAA is illustrated by the Portulaca Verbena Thunbergia levels during winter. large number of rooting products 36 GPN August 2005 crop cultivation should be regulated appropriately, if Figure 2. Commercially available rooting hormones for herbaceous plant propagation. Trade name Source Formulation Ingredient the propagation medium is too satu- rated (low oxygen) or light levels are Chryzopon ACF Chemiefarma Powder (talc) 0.1-8 percent IBA too intense, rooting is inhibited. C-mone Coor Farm Liquid (isopropyl alcohol) 1 and 2 percent IBA Supply Services, Inc. HORMONE C-mone K Coor Farm Liquid (isopropyl alcohol) 1 percent KIBA CONCENTRATIONS Supply Services, Inc. Generally speaking, auxin- C-mone K+ Coor Farm Liquid (isopropyl alcohol) 1 percent KIBA + based rooting products are applied Supply Services, Inc. 0.5 percent NAA at concentrations of 500-1,500 ppm Dip ‘n’ Grow Astoria-Pacifica Inc. Liquid (alcohol) 1 percent IBA + for herbaceous and softwood cut- 0.5 percent NAA + boron tings. In addition, rates between Hormex Brooker Chemical Corp. Powder (talc) Rooting Powder — 1,000 and 3,000 ppm may be used 0.1-4 percent IBA for woodier tissue, but the maxi- Hormex Brooker Chemical Corp. Liquid Hormex Concentrate — mum recommended concentra- 0.013 percent IBA + tions are not more than 5,000 and 0.24 percent NAA + 10,000 ppm for semi-hardwood vitamin B-1 and hardwood cuttings, respective- Hormodin E.C. Geiger, Inc. Powder (talc) 0.1, 0.3 and 0.8 percent IBA ly. When optimal treatments are Hormo-Root Rockland Chemical Co. Powder (talc) 0.1-4.5 percent IBA applied, cuttings will tend to have IBA Water Soluble Salts Hortus USA Corp. Inc. Liquid 20 percent IBA the following characteristics: Basal portion of cutting shows Rhizopon Hortus USA Corp. Inc. Powder and 0.1, 0.3 and 0.8 percent IBA water-soluble tablet form some swelling, callus tissue forms and root initials emerge just above Stim-Root Plant Products Co. Ltd. Powder (talc) 0.1 and 0.4 percent IBA the cutting base. Woods Rooting Compund Earth Science Liquid (ethanol) 1.03 percent IBA + Products Corp. 0.56 percent NAA Care should be taken with root-± ing hormones because over- 38 GPN August 2005 crop cultivation Write in 780 Top: Cutting bases can be sprayed with rooting hormones; efficiency is increased when they are treated in bundles. Bottom: K-IBA is a water-soluble rooting hormone that has enormous potential with floriculture crops. (Photos courtesy of James Gibson) application of some formulations better to use a small portion of the can cause damage to the cutting hormone mixture in a separate con- base. Formulations dissolved in tainer, away from the stock batch alcohol are more prone to cause with frequent changes. This will burn or dehydrate plant tissue. minimize the potential for disease Auxin in excessive concentrations spread and cross contamination. may result in inhibition of bud Powders. Auxin-based rooting development, yellowing of leaves, hormones may be mixed with talc leaf abscission, blackening of stems and applied to the base of cuttings. and even death of cuttings. It has The cuttings are dipped in the pow- also been reported that misapplica- der, then lightly tapped to remove tion to leaves may result in curling excess chemical. To increase adhe- or other distortion of plant growth. sion of powder to cutting bases, stem tissue can be re-cut or dipped in APPLICATION water or alcohol before application. There are several accepted meth- However, this will lead to a more ods of application for growers rapid deterioration of the rooting wishing to utilize rooting hormones hormone batch and may increase the in their propagation practices. potential for disease spread. When dipping cutting bases into a Powdered forms of rooting hor- rooting hormone, better efficiency mones are generally less effective is maintained with dipping several than liquid formulations applied at cuttings at once, rather than dip- the same concentration. Auxin± ping them individually. It is also uptake by the cutting base is often 40 GPN August 2005 crop cultivation Influence of rooting hormones on propagation of pentas (top) and mandevilla (bottom) left to right: untreated, K-IBA at 1,000 ppm, K-IBA at 5,000 ppm, K-IBA at 10,000 ppm, Dip ‘n’ Grow – semihardwood concentration, Dip ‘n’ Grow – softwood concentration, Hormodin #1, Hormodin #2 and Hormodin #3. (Photo courtesy of James Gibson) inhibited by the texture of the stem Other formulations. Water sol- (smooth vs. rough) or immediate uble formulations of rooting hor- removal of talc from the cutting tis- mones such as K+ or potassium sue when inserted into the propa- salt formulations of IBA and NAA gation medium. However, talc- have traditionally been used by based products have the advantage propagators of woody ornamen- of being less toxic, more sanitary tals and show promise for herba- than the liquid formulations and ceous plant propagation. These quicker and easier to apply. These compounds are readily dissolved factors may ultimately make pow- in water rather than alcohol, ders more cost effective. which tends to make their use by Quick-dip Solutions. Quick- growers safer and easier. dip solutions follow the same Post-planting sprays. As an general principle of application alternative to dipping cuttings in as powders, in that they are talc or liquid, rooting hormones can auxin-based products mixed with be applied to cutting bases or the a carrier (usually alcohol or foliage as a spray. Pre-plant foliar water) and are applied to the sprays directed toward the stem base of the cutting.